(1) Field of the Invention
The present invention relates to an ink jet recording head which jets ink in the form of a droplet from an ink nozzle by utilization of a piezoelectric effect.
(2) Description of the Related Art
An ink jet recording head for jetting ink in the form of a droplet from an ink nozzle by utilization of a piezoelectric effect has been well known in the art. Examples of such ink recording heads are disclosed in U.S. patent application Nos. 4,819,614 and 4,752,788.
FIG. 1 is a sectional view of a conventional ink jet recording head. As shown in FIG. 1, a plurality of concave-shaped ink cavities 52 are formed on one surface of a piezoelectric plate 51; the piezoelectric plate 51 made of piezoelectric materials is disposed between adjacent concave-shaped ink cavities; and a convex portion 53 made of piezoelectric materials is formed to conform the concave shape of the concave-shaped ink cavity 52. The top of the concave-shaped ink cavities is covered with a cover plate 54.
Each of the concave-shaped ink cavities 52 matching with the convex portion 53 comprises two deep grooves (b) for spacing the piezoelectric plate 51 and the convex portion 53 from each other and a shallow groove (a) between the deep grooves (b). An electrode 55 is provided on the bottom of the piezoelectric plate 51; and an electrode 56 is provided on the convex-portion 53. Also, a nozzle 57 is formed on the same surface of the piezo-electric plate 51 as the ink cavity to have the nozzle be coupled with the corresponding ink cavity.
When a voltage is applied across a selected pair of electrodes 55 and 56 in the ink jet recording head thus constructed, the convex portion 53 is deformed to change the volume of the ink cavity 51; as a result, ink in the ink cavity is jetted from the nozzle. The ink jet recording head, however, has the following drawbacks.
As was described with referring to FIG. 1, two deep grooves and one shallow groove are constructed in the piezoelectric plate 51; and the manufacturing cost of this piezoelectric plate 51 is relatively expensive. Particularly in the case when it is required to arrange ink cavities at a high density, the width of each groove (b) becomes as narrow as some xcexcm, and it is considerably difficult for the present manufacturing technique to form such ink cavities in a piezoelectric plate.
Further, between adjacent ink cavities is provided a bulkhead made of piezoelectric materials, accordingly, an electric field formed across the electrodes 55 and 56 may vibrate the bulkhead between the ink cavities. As a result, the volume of the adjacent ink cavity is changed due to cross-talk between the ink cavities. As a result, around a nozzle is stained with leakage of ink from the adjacent ink cavity, whereby the ink jetting direction is fluctuated.
The cross-talk between ink cavities may be prevented; however, since the convex-portion 53 and the bulkhead are provided as an integral unit, deformation of the convex portion 53 may cause deformation of the bulkhead. Consequently, effective ink jetting is hindered; otherwise, a high-speed response ability is retarded.
Further, the vibration of the convex portion 53 moves ink into the groove (b), the groove (b) for spacing the convex portion 56 and the bulkhead 51; therefore, ink jetting effect is degraded; or ink penetrates the convex portion 53 from its side walls, as a result of which a bulk resistance is lowered. Accordingly, a drop of voltage or an electrolysis of ink occurs. Also, a cavitation of ink occurs at the groove (b) due to the vibration of the piezoelectric plate, as a result of which effective jetting by utilization of pressure is hindered.
Accordingly, it is an object of the present invention to provide an ink jet recording head which can be readily manufactured at a low manufacturing cost, and to achieve effective ink jetting by preventing cross-talk between ink cavities.
Also it is another object of the present invention to provide an ink jet recording head which enables effective jetting of ink which is pressured due to vibration of an piezoelectric member by preventing a drop of an effective voltage and a cavitation.
The above objects may be fulfilled by a multi-nozzle ink jet head comprising a first member including a plurality of first convex parts disposed in line on a part of its surface, in which at least a part of the first convex part is a piezoelectric element, a second member made of non-piezoelectric materials, including a plurality of concave parts which correspond to the first convex parts, and a second convex part disposed between every two adjacent concave parts, in which the second member is engaged with the first member by inserting each second convex part between a couple of adjacent first convex parts and forming an ink cavity between a bottom of each concave part and a top of the respective first convex part, and a plurality of electrodes being applied to the piezoelectric element included in the first convex part, in which each electrode deforms the respective piezoelectric element by applying a voltage to the same and jets ink in the ink cavity from an ink nozzle.
The first convex part may be inserted into the non-piezoelectric concave part in such a manner that either of them can be movable to the other.
A first gap may be formed between a side surface of the first convex part and a side surface of the non-piezoelectric concave part.
The second filling member for filling the second gap may include a filling and adhesive member, the surface of the first member including the convex part may be covered with a protection film and the protection film may be adhered to the convex part with the filling and adhesive member, and the second filling member may include a part of the protection film besides the filling and adhesive member.
The first member may include a base member and a piezoelectric chip which is disposed on the base member, the piezoelectric chip being equivalent to the piezoelectric element.
The electrodes may be disposed on surfaces of the corresponding piezoelectric chip, the surfaces opposing to each other.
Any one of the piezoelectric chips may be a lamination of piezoelectric layers.
The piezoelectric element may be made of piezoelectric materials and the first member is an integral unit.
Conductive treatment may be applied to the first member except the first convex part.
The piezoelectric element included in the first convex part may be polarized in the same direction as an electric field formed by applying a voltage across the electrodes, and the polarization direction may be substantially perpendicular to an ink jetting direction.
A front end of each ink cavity along with the ink jetting direction may be covered with a front member in which the ink nozzles are formed, a back end of each ink cavity along with the ink jetting direction may be blocked with a block member, and a ink supplying slit communicating with the ink cavity may be formed in the second member.
A non-return valve may be constructed to the ink supplying slit.
According to this construction and manufacturing method, the first member can be readily formed; accordingly the manufacturing cost is reduced by large.
Since the bulkhead between the adjacent ink cavities is made of non-piezoelectric materials, it is not vibrated by the electric field generated by application of a voltage across a selected pair of electrodes. Also, since the bulkhead and the first convex part in the first member are formed independently from each other, a cross-talk can be highly suppressed.
The second object may be fulfilled by the multi-nozzle ink jet head further including a first filling member for filling the first gap.
One surface of the first member which includes the convex part may be covered with a protection film, and the first filling member may consist of a part of the protection film.
A second gap may be formed between a top surface of the non-piezoelectric second convex and the first member, and the second gap may be filled with a second filling member.
In this construction, by filling the gap between the first convex part in the first member and the sides of the concave part in the second member, insertion of ink is prevented; accordingly, ink jetting efficiency is improved. Further, by doing so, ink can be prevented from penetrating the first convex part in the first member through its side walls, as a result of which a drop of effective voltage and an electrolysis of ink are prevented. Also, no cavitation occurs at the bulkhead, so that ink jet efficiency is improved
Also the second object may be fulfilled by a multi-nozzle ink jet head comprising a plurality of ink cavities disposed in line, in which adjacent ink cavities are separated by a wall, a plurality of piezoelectric elements, each of which protrudes into each ink cavity and a space exists between itself and the wall, a plurality of electrodes which correspond to each piezoelectric element, and deforms the corresponding piezoelectric element by applying a voltage thereto so that ink in the ink cavity is jetted, and a filling member for filling the space between the piezoelectric element and the wall.
Also in this construction, the gap between the sides of the piezoelectric convex part and the bulkhead is filled with the filling member; accordingly, the above effects can be achieved.
The first object may be fulfilled by a method of producing a multi-nozzle ink jet head comprising the steps of producing a first member where a plurality of first convex parts are disposed in line, and at least a part of the first convex part is a piezoelectric element, producing a second member from piezoelectric materials, which includes a plurality of concave parts corresponding to the first convex parts, and a second convex part being disposed between adjacent concave parts, engaging the first member and the second member in such a manner that first convex part is inserted into the non-piezoelectric concave part, and an ink cavity is formed between a top of the first convex part and a bottom of the non-piezoelectric concave part.
The method may further comprise the step of forming a protection layer on one entire surface of the first member which includes the first convex part.
The method of may further comprise the step of totally covering one surface of the first member which includes the first convex part with a film.
The step of producing the first member may be the step of laying piezoelectric materials on a base member and cutting it into a predetermined shape so that the first member where the piezoelectric elements are disposed on the base member in line is produced.